L2TP dialup is successful but communication on the private network fails

The possible causes are as follows:
- The intranet host is enabled with the firewall.
- The local subnet and remote intranet are on the same network segment.
- The address for L2TP dialup access and addresses of LAN users are on the same network segment, but proxy ARP is disabled.
- The MTU on the virtual interface is set improperly. It is recommended that this MTU plus all the header lengths should not exceed the interface MTU. Otherwise, if a device does not support fragmentation, packets will be discarded.
- The TCP MSS on the virtual interface is set improperly. Ensure that the MSS plus all the header lengths should not exceed the interface MTU. Otherwise, packet transmission is affected.
- LCP renegotiation is not configured.
- Routes are unreachable.
- Tunnel authentication is not configured.
- Data protected by IPSec does not match an ACL.

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